ATX PSU input voltage range

[jasonbay13]

the input range is pretty wide for power supplies and can operate as low as 90-ish volts on some. that is still too high for what i'm looking for. is it possible to modify one that can work off 48v? i have a dozen or so laying around in the 150-500w range. i'm thinking it could be done by re-winding the primary to half the turns, but will probably need resistors for the switching transistors changed also.
or else i'm way off and it would need to be re-designed completely :/

[budm]

Re: ATX PSU input voltage range

When you lower the input Voltage the input current will increase to maintain the output power (it is regulated power supply), so it is not that simple.
For example (lets assume no conversion loss for easy calculation) you have regulated power supply that has regulated 10V output and 10A of current capability which will be 100W.
So if the input is 100V then the input current will be 1A so the switching device has to be able to handle at least 1A, so if you drop the input to 50v then the input current will have to be increase to 2A so the switching device and the transformer winding will also have to be able to handle 2A.

[jasonbay13]

Re: ATX PSU input voltage range

wouldnt that be as simple as the power supply delivering half its capacity due only to the primary transformer and switcher current? which would be acceptable for what use i have for it if it is possible and doesnt require more than resistors and transformer. though i plan on giving it ~50vdc so that would be a little less than half.

or maybe even simpler would be a dc-dc voltage doubler, then it would be right in the operating range, but google searches come up nil for anything over a few watts or require special ics.

[mariushm]

Re: ATX PSU input voltage range

No, most ATX power supplies can work with a wide range of input voltage like 80v AC - 230v AC which rectified means a DC waveform with peaks that go to at least about 110v DC and maximums up to around 330v DC.

Modern ATX power supplies have Active PFC which basically boosts whatever the input voltage it receives to about 350-400c DC.
Then there's transistors or mosfets which - controlled by a custom chip that receives feedback from the secondary side - turn on and off for various amounts of time (depending on how much current is used on the secondary side), sending a number of pulses through the transformer and that's how you get some DC voltage on the secondary side which then gets regulated into 12v, 5v and 3.3v
If the current consumption on the output is higher, the number of pulses (turn on and off) per second is higher, with lower current you get fewer pulses.

So basically you could try feeding 40-60v DC to such power supplies but my guess is the Active PFC circuit won't start or it would blow something up due to too high peak input currents

There's no point trying when there's a HUGE selection of power supplies designed from the start to work with relatively low DC voltages at the input, see this page for example : http://www.digikey.com/product-searc...verters/590047

[CapLeaker]

Re: ATX PSU input voltage range

Why not upping the 48V AC with a 1:2 step up transformer, then hook up the PSU to it? Then you end up with 96V AC.
Maybe a voltage doubler circuit?

[jasonbay13]

Re: ATX PSU input voltage range

Why not upping the 48V AC with a 1:2 step up transformer, then hook up the PSU to it? Then you end up with 96V AC.
Maybe a voltage doubler circuit?

only problem here is the 48v is dc from a battery.

btw, took a look at those dc>dc converters to go from 48 to 12. like 100 usd for the cheapest one.

[budm]

Re: ATX PSU input voltage range

48VDC! That is basically the same as feeding it with 34VAC.

[CapLeaker]

Re: ATX PSU input voltage range

at this point you can almost buy a 48V ATX PSU.

[Per Hansson]

Re: ATX PSU input voltage range

AFAIK you can't feed a full range APFC PSU with DC voltage.
It only accepts AC input.
An old passive PFC or no PFC PSU will gladly do it though.
The DC just goes through the rectifier unmodified, well, I guess it would protect against reversed polarity